I'd advise you to revise papers from may/june 2007 onwards as this is the new syllabus. papers earlier than this is the old syllabus where paper 5 included an actual practical experiment. the new papers 5 has do actual practical it is more about planning, evaluation, analysis and treatment of errors. search for the CIE A2 practical skills booklet on google, download it and start from there. since time is running out though, start doing past papers and reading examiner reports, they help alot.